Add Docker image: GHCR multi-arch (linux/amd64 + arm64)

Multi-stage Dockerfile (golang:1.23-alpine → distroless/static:nonroot)
bakes the version string via --ldflags. GitHub Actions docker.yml workflow
publishes to ghcr.io/unirate-api/unirate-cli on every main-branch push
and v* tag; Docker Hub enabled by setting DOCKER_HUB_USERNAME Actions
variable + DOCKER_HUB_TOKEN secret.

Author: rob-browncc

.dockerignore

@@ -0,0 +1,3 @@
+.github/
+examples/
+*.md

.github/workflows/docker.yml

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+name: Docker
+
+on:
+  push:
+    branches: [main]
+    tags: ["v*"]
+
+permissions:
+  contents: read
+  packages: write
+
+jobs:
+  docker:
+    name: Build and push
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Log in to Docker Hub
+        if: ${{ vars.DOCKER_HUB_USERNAME != '' }}
+        uses: docker/login-action@v3
+        with:
+          username: ${{ vars.DOCKER_HUB_USERNAME }}
+          password: ${{ secrets.DOCKER_HUB_TOKEN }}
+
+      # Build the image list dynamically so Docker Hub is only included when
+      # the DOCKER_HUB_USERNAME Actions variable is set on the repo.
+      - name: Compute image list
+        id: imgs
+        run: |
+          IMGS="ghcr.io/unirate-api/unirate-cli"
+          if [ -n "$DH_USER" ]; then
+            IMGS="$IMGS"$'\n'"docker.io/$DH_USER/unirate-cli"
+          fi
+          printf 'list<<EOF\n%s\nEOF\n' "$IMGS" >> "$GITHUB_OUTPUT"
+        env:
+          DH_USER: ${{ vars.DOCKER_HUB_USERNAME }}
+
+      - name: Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ steps.imgs.outputs.list }}
+          tags: |
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=raw,value=latest,enable={{is_default_branch}}
+          labels: |
+            org.opencontainers.image.title=unirate-cli
+            org.opencontainers.image.description=Currency exchange rates, conversion, and VAT from the UniRate API
+            org.opencontainers.image.url=https://github.com/UniRate-API/unirate-cli
+            org.opencontainers.image.licenses=MIT
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          build-args: |
+            VERSION=${{ steps.meta.outputs.version }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max

Dockerfile

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+FROM golang:1.23-alpine AS builder
+WORKDIR /build
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+ARG VERSION=dev
+RUN CGO_ENABLED=0 GOOS=linux go build \
+    -trimpath \
+    -ldflags="-s -w -X main.version=${VERSION}" \
+    -o unirate .
+
+FROM gcr.io/distroless/static-debian12:nonroot
+COPY --from=builder /build/unirate /unirate
+ENTRYPOINT ["/unirate"]

README.md

@@ -47,6 +47,16 @@ go install github.com/UniRate-API/unirate-cli@latest
 **Binaries:** prebuilt archives for linux/macOS/windows (amd64 + arm64) are
 attached to each [GitHub release](https://github.com/UniRate-API/unirate-cli/releases).
 
+**Docker** (linux/amd64 + arm64):
+
+```bash
+docker run --rm -e UNIRATE_API_KEY="$UNIRATE_API_KEY" \
+  ghcr.io/unirate-api/unirate-cli:latest convert 100 USD EUR
+```
+
+Images are published to the [GitHub Container Registry](https://github.com/UniRate-API/unirate-cli/pkgs/container/unirate-cli)
+on every release and on pushes to `main`.
+
 ## Authentication
 
 Every command needs an API key. Set it once in your environment: